High authority stability and control augmentation system

ABSTRACT

A system and method of increasing the control authority of redundant stability and control augmentation system (SCAS) actuators by utilizing feedback between systems such that one system may compensate for the position of a failed actuator of the other system. Each system uses an appropriate combination of reliable and unreliable inputs such that unreliable inputs cannot inappropriately utilize the increased authority. Each system may reconfigure itself when the other system actuator fails at certain positions so that the pilot or other upstream input maintains sufficient control authority of the aircraft.

BACKGROUND 1. Field of the Invention

The present application relates generally to flight control systems, andmore specifically, to an aircraft flight control system for allowing anaugmentation system to have higher authorities, for example up to fullauthority, on an aircraft that has a mechanical flight control system.

2. Description of Related Art

Previous attempts to provide higher authority on Stability and ControlAugmentation Systems (SCAS) have relied upon mechanical limits. Forexample, some SCAS actuators are mechanically limited in authority tomitigate the effects of a failure resulting in actuator seizure orundesired motion. Other SCAS actuators use spring mechanisms to centerthe SCAS actuators upon a failure. Actuator authority is limitedmechanically to mitigate the effects of undesired motion resulting froma failure including the sudden recentering which will result if afailure occurs while the actuator is working near its extreme position.None of the previous attempts provide high authority.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the embodiments of thepresent application are set forth in the appended claims. However, theembodiments themselves, as well as a preferred mode of use, and furtherobjectives and advantages thereof, will best be understood by referenceto the following detailed description when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a side view of a rotary aircraft;

FIG. 2 is a schematic of the high authority stability and controlaugmentation system according to the preferred embodiment of the presentapplication;

FIG. 3a is a schematic of the flight control system according to thepreferred embodiment of the present application; and

FIG. 3b is a schematic of the processor according to the preferredembodiment of the present application.

While the system and method of the present application are susceptibleto various modifications and alternative forms, specific embodimentsthereof have been shown by way of example in the drawings and are hereindescribed in detail. It should be understood, however, that thedescription herein of specific embodiments is not intended to limit theinvention to the particular embodiment disclosed, but on the contrary,the intention is to cover all modifications, equivalents, andalternatives falling within the spirit and scope of the process of thepresent application as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The system and method of the present application overcomes theabovementioned limitations commonly associated with conventional SCASactuators. The system improves optionally manned aircraft by fixing theinput controls and using the SCAS with high authority to control theaircraft in flight. Further description and illustration of the highauthority stability and control system and method is provided in thefigures and disclosure below.

It will of course be appreciated that in the development of any actualembodiment, numerous implementation-specific decisions will be made toachieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

The system and method of the present application will be understood,both as to its structure and operation, from the accompanying drawings,taken in conjunction with the accompanying description. Severalembodiments of the system are presented herein. It should be understoodthat various components, parts, and features of the differentembodiments may be combined together and/or interchanged with oneanother, all of which are within the scope of the present application,even though not all variations and particular embodiments are shown inthe drawings. It should also be understood that the mixing and matchingof features, elements, and/or functions between various embodiments isexpressly contemplated herein so that one of ordinary skill in the artwould appreciate from this disclosure that the features, elements,and/or functions of one embodiment may be incorporated into anotherembodiment as appropriate, unless described otherwise.

Referring now to the drawings, FIG. 1 shows a rotary aircraft utilizingthe flight control system of the present application. FIG. 1 shows aside view of a helicopter 101. However, it will be appreciated that thecontrol system is easily and readily adaptable for use with other typesof rotary aircraft, i.e., helicopter 101, operating at various speedsand with or without a fixed lateral cyclic control.

Helicopter 101 comprises a rotary system 103 carried by a fuselage 105.One or more rotor blades 107 operably associated with rotary system 103provide flight for helicopter 101 and are controlled with a plurality ofcontrollers within fuselage 105. For example, during flight a pilot canmanipulate the cyclic controller 109 for changing the pitch angle ofrotor blades 107, thus providing lateral and longitudinal flightdirection, and/or manipulate pedals 111 for controlling yaw direction.Helicopter 101 includes a dual Automatic Flight Control System (AFCS).

For ease of description, some of the required systems and devicesoperably associated with the present control system are not shown, i.e.,sensors, connectors, power sources, mounting supports, circuitry,software, and so forth, in order to clearly depict the novel features ofthe system. However, it should be understood that the system of thepresent application is operably associated with these and other requiredsystems and devices for operation, as conventionally known in the art,although not shown in the drawings.

Referring now also to FIG. 2 in the drawings, a schematic of a highauthority stability and control augmentation system 203 is shown. Thehigh authority stability and control augmentation system 203 allows forsignificantly enhanced aircraft automation by allowing an augmentationsystem to have higher authorities (up to full authority) on an aircraftthat has a mechanical flight control system. The high authoritystability and control augmentation system 203 is comprised of a firstflight control computer (FCC) 205, a second FCC 207, a first actuator209 typically a SCAS actuator, a second actuator 211 typically a SCASactuator, and a flight control actuator 213. As typical between FCC'sthe first FCC 205 is in communication with the second FCC 207.

First actuator 209 is summed with second actuator 211 which both aresummed with input 215. The summation can be mechanical, for example, theactuators can move a control rod. Alternatively, the summation can beelectrical, for example, a digital or analog signal of the actuators canbe summed together with other signals. Preferably, input 215 is from thepilot input into the controls, such as lateral or longitudinal cycliccontrols 109; however other upstream inputs to the aircraft controlaxis, such as trim actuators are contemplated by this application. Itshould be apparent that each axis of control requires a dual system(System 1 and System 2) 203 and that for clarity sake only a single axisof controls is shown. Furthermore, each system (1 and 2), at least inregard to flight critical functionality such as rate sensor inputs,processing, and output monitoring, may be dual and self-checking. Anydisagreement within either system can allow that system to shut down itsassociated SCAS actuator and therefore no single failure would result inerroneous movement of the SCAS actuator. Rather, single failures withineither system would result in the SCAS actuator associated with thefailed system holding fixed in position. First actuator 209 is dualcommanded from the first FCC 205 by a first command 217 a and a secondcommand 217 b each being sourced from one of two self checkingprocessors within the first FCC 205. First actuator 209 is smart andalso self checking and therefore can compare the first command 217 a tothe second command 217 b and can use other means to otherwise monitorthe health of the commanding FCCs outputs. In one embodiment, firstactuator 209 provides dual status and positional feedback 219 to thesecond FCC 207. While comparing first command 217 a to the secondcommand 217 b, if the first actuator 209 senses a significantdisagreement between the first command 217 a and the second command 217b or any other indication of failures of the commanding FCC such as lackof command updates, the actuator 209 fails itself fixed in place. If thefirst actuator 209 fails fixed in place the second FCC 207 may thencompensate for the fixed position of the first actuator 209 by changingits commands to second actuator 211. For example, as long as the firstactuator 209 is working properly the status signals 219 are held to ahigh voltage. If the first actuator 209 fails the status signals 219 aredriven low. The second FCC 207 receiving the failed status 219 from thefirst actuator 209 and utilizing the last known position information219, may command the second actuator 211 to a different position tomitigate the failed position of the first actuator 209 so that thecontrol input 215 retains sufficient control authority of the aircraft.Second actuator 211 is dual commanded 221 from the second FCC 207.Second actuator 211 provides dual status and positional feedback 223 tothe first FCC 205. Inputs 225 to first FCC 205 and to second FCC 207 arecomprised of typical inputs to FCCs such as: positional information fromthe controls via displacement transducers; attitudes and attitude rates;pitch rates; airframe accelerations; airspeed; engine parameters; rotorparameters; and transmission parameters. Similarly to above, if thesecond actuator 211 fails, the first FCC 205 then compensates for thefailed second actuator 211.

Referring now also to FIG. 3a in the drawings, a schematic of animproved FCC 205 having a high authority stability and controlaugmentation system 203 is illustrated. The first FCC 205 includes afirst processor 235 and a second processor 239. First processor 235provides the first command 217 a to the first actuator 209, and thesecond processor 239 provides the second command 217 b to the firstactuator 209. The two processors compare their respectiveinterpretations of inputs 225 and computed outputs 217 a and 217 b. Anydisagreement, will force SCAS actuator 1 to fail fixed. In oneembodiment, this can be accomplished by sending commands that arerecognized by the first actuator 209 as commands to fail fixed.

In the preferred embodiment the SCAS actuators are SMART and compare thefirst command to the second command. In an alternative embodiment theFCCs control the position of the SCAS actuators directly and status andposition feedback to the other system is therefore sourced from theFCCs. In such case, the internal redundant configuration of the SCASactuators would be accomplished within the redundant configuration ofthe FCCs.

Referring now also to FIG. 3b in the drawings, a schematic of thealgorithms implemented within each processor 235 and 239 is illustrated.Located inside each processor 235 and 239 are a first set ofcomputational algorithms 253, a second set of computational algorithms257, limits 261, and a summation 265. Preferably computationalalgorithms 253 are software based however in an alternative embodimentcomputational algorithms 253 are comprised of analog hardware monitoringand responding to inputs 225. Limits 225 are grouped into trusted inputsand into un-trusted inputs. The first computational algorithms 253utilize input type 225 a or trusted inputs. Input type 225 a consists ofinputs that are monitored sufficiently and robustly enough to guaranteethe validity of the data supplied to the first computational algorithm253. Examples of monitored inputs 225 a include attitude rates and pitchrates. First computational algorithm 253 determines a part of theactuator command 217 a dependent upon the specific input from the inputtype 225 a. For example the first computational algorithm 253 adjuststhe actuator command 217 a based upon a falling attitude rate. Inputtypes 225 b or un-trusted inputs are inputs that are not necessarilyreliable and are supplied to the second set of computational algorithms257. An example of an unreliable input 225 b may be airspeed. Secondcomputational algorithm 257 determines a part of the actuator command217 a dependent upon the specific input from the input type 225 b.Limits 261, limit the contribution of the output of the second set ofcomputational algorithms 257 to the actuator commands 217 a and 217 b.Limit 261 is configured to limit the unreliable input 225 b to amagnitude that has been determined safe for the helicopter 101 were itto be incorrect data. In another embodiment, limits to inputs 225 b mayexist prior to computational algorithms 257. In yet another embodiment,additional computational algorithms may exist at the output of thesumming element 265. It is the appropriate combination of these twoclasses of inputs 225 a and 225 b that allow the system 203 theadvantages resulting from higher authority while maintaining safety.

When the actuator in one system fails as a fixed position, the remainingsystem, based on the status and position feedback from the failedsystem, may configure new position command limits such that anysubsequent failure in the remaining system would result in a netposition in which the sum of both actuator positions is within a rangesufficient for the pilot or other upstream input to retain sufficientcontrol of the aircraft. Upon detection of the first failure, theremaining system may act to command the unfailed actuator to within thenewly established limits if necessary to accomplish the objective.

The system and method described herein solves the limitation of limitedautomatic control authority by incorporating feedback, mitigationalgorithms, and computation limiting to a traditional mechanicallylimited dual system.

It is apparent that a system and method with significant advantages hasbeen described and illustrated. The particular embodiments disclosedabove are illustrative only, as the embodiments may be modified andpracticed in different but equivalent manners apparent to those skilledin the art having the benefit of the teachings herein. It is thereforeevident that the particular embodiments disclosed above may be alteredor modified, and all such variations are considered within the scope andspirit of the application. Accordingly, the protection sought herein isas set forth in the description. Although the present embodiments areshown above, they are not limited to just these embodiments, but areamenable to various changes and modifications without departing from thespirit thereof.

What is claimed is:
 1. A method for increasing the authority of astability and control augmentation system, comprising: providing a firstactuator; grouping robust inputs into a first group of inputs; groupingnon-robust inputs into a second group of inputs; processing the firstgroup of inputs into trusted commands for the actuator; processing thesecond group of inputs into un-trusted commands for the actuator;providing a set of limits for the un-trusted commands; limiting thecontribution of the un-trusted commands based on the set of limits toform limited un-trusted commands; and summing the trusted commands withthe limited un-trusted commands, wherein the robust inputs aremonitored.
 2. The method according to claim 1, wherein the step ofsumming the trusted commands with the limited un-trusted commands isutilized to move the first actuator.
 3. The method according to claim 1,wherein the robust inputs are attitude rates.
 4. The method according toclaim 1, wherein the robust inputs are pitch rates.
 5. The methodaccording to claim 1, wherein the non-robust inputs are airspeeds.
 6. Arotary aircraft having a rotary system carried by a fuselage, the rotarysystem comprising: a first flight control computer carried by thefuselage, the first flight control computer having; a first processorfor commanding a first actuator along a first axis; and a secondprocessor for commanding the first actuator along the first axis; asecond flight control computer carried by the fuselage; a first actuatorcommanded by the first flight control computer for manipulating therotary system along the first axis; a second actuator commanded by thesecond flight control computer for manipulating the rotary system alongthe first axis; and a third actuator for manipulating the rotary systemalong the first axis; wherein the first actuator compares commands fromthe first processor of the first flight control computer to commandsfrom the second processor of the first flight control computer to find afailure in the first actuator; and wherein an output of the firstactuator is summed with an output of the second actuator and summed witha control input for manipulating the rotary system with full authorityin only the first axis by controlling the third actuator.
 7. The rotaryaircraft according to claim 6, wherein the first and second processorsin the first flight control computer group inputs by reliability.
 8. Therotary aircraft according to claim 7, wherein the first actuator islimited by unreliable inputs.
 9. The rotary aircraft according to claim6, wherein the failure in the first actuator forces the first actuatorfixed.
 10. The rotary aircraft according to claim 9, wherein the secondactuator adjusts automatically due to, the failure in the firstactuator.
 11. A rotary aircraft having a rotary system carried by afuselage, the rotary system comprising: a first flight control computercarried by the fuselage, the first flight control computer having; aplurality of processors; a second flight control computer carried by thefuselage, the second flight control computer having; a plurality ofprocessors; a first actuator commanded by the first flight controlcomputer for manipulating the rotary system along a first axis; a secondactuator commanded by the second flight control computer formanipulating the rotary system along the first axis; and a thirdactuator for manipulating the rotary system along the first axis;wherein the first actuator compares commands between the processors ofthe first flight control computer to find a failure in the firstactuator; and wherein an output of the first actuator is summed with anoutput of the second actuator and summed with a control input formanipulating the rotary system with full authority in only the firstaxis by controlling the third actuator.
 12. The rotary aircraftaccording to claim 11, wherein the plurality of processors in the firstflight control computer group inputs by reliability.
 13. The rotaryaircraft according to claim 12, wherein the first actuator is limited byunreliable inputs.
 14. The rotary aircraft according to claim 12,wherein the second actuator adjusts automatically due to the failure inthe first actuator.
 15. The rotary aircraft according to claim 11,wherein the failure in the first actuator forces the first actuatorfixed.